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From the outside in: How eczema could lead to food allergies …

New research suggests that babies might become sensitive to food through damaged skin, for example in eczema.

You wouldn’t think you could develop a food allergy through your skin, but according to new research a weaker skin barrier as caused by eczema could lead to food sensitivity.

Researchers from King’s College London and a Wellcome Trust-funded lab at the University of Dundee, studied 600 three-month-old babies. They found that babies with weaker skin, especially those with a form of eczema called atopic dermatitis, were over six times more likely to be sensitive to certain foods like egg, cow’s milk and peanut than their healthy-skinned peers, meaning that they had a positive allergy test in reaction to these foods.

The research, published in the Journal of Investigative Dermatology, was part of the EAT (Enquiring About Tolerance) study, which investigates whether introducing common allergens like peanuts into the diet at 3 (as opposed to 6) months might help reduce food allergies later on. Allergies occur when the immune system responds to a substance (allergen) that is actually harmless, attacking it. All the children involved were breastfed from birth, so had never eaten any solid food, let alone the allergenic food they were exposed to here. Therefore, any sensitivity to the food could not have been because immune cells in the digestive system were exposed to allergenic food. Immune cells elsewhere must have been exposed to the allergens. The suggestion is that with a weakened barrier to the outside world (like the thinner skin found in eczema), allergens present in the environment can make contact with immune system cells that are found in the skin, triggering an allergic immune response. So food allergies develop from the outside in, starting at the skin.

The link between eczema and allergies (including asthma) has long been known, but this is one of the first studies showing this effect in young babies and directly assessing the effectiveness of the skin barrier. Researchers tested food sensitivity by using a tiny needle containing a sample of the allergenic food to prick an area of the baby’s skin. If the skin reacted by forming a swelling, this counted as food sensitivity. The food causing the most reactions was egg white, followed by cow’s milk and peanut. If a baby’s eczema was more severe, so was their reaction to the food.

Of course, food sensitivity doesn’t necessarily lead to a clinical allergy. Nevertheless, the findings have implications for both the study of eczema and food allergies. Says Dr Carsten Flohr, first author on the study, “If we can repair the skin barrier and treat atopic dermatitis, we might also be able to reduce the risk of food allergies.”

Furthermore, the skin is not the only place where food allergies will develop. Children can have a food sensitivity without having eczema first. Other genes will also have an impact on the development of both eczema and food sensitivity, reacting with environmental factors like hygiene, water hardness and bacteria found on the skin. Part of EAT’s remit is to follow these children up to see if, as the researchers suspect, exposure to these allergens earlier on in life, at three months, may help reduce future allergies – a practice that goes against current government recommendations.

Though it seems counterintuitive that being fed potential allergens early could reduce later allergies, while exposure through the skin increases them, Dr Flohr says it makes sense if you think evolutionarily. “Anything that reaches the immune system from across the digestive tract is seen as ‘good’ because the food given to us by our parents is not likely to be harmful.” It’s different for things coming through the skin, which tend to be ‘bad’ things like parasites. Thus, immune cells in the gut might see most things they come across as harmless, those in the skin will label anything they’re exposed to as harmful.